Isomerization of saturated hydrocarbons in the presence of a polynuclear condensed ring compound as cracking inhibitor



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18 Claims. (Cl.-26ll-'683.5)

This invention relates to an isomerizatio'n process and more particularly to the iso'me'rization of "saturated hydrocarbons in the presence of hydrogen.

It is frequently desirable to isomerize saturated hydrocarbons such as the paraffinic and 'naphthenic hydro carbons and convert one isomer to another. For ex" ample, n-heptane or n-octane are poor fuels for internal combustion engines, whereas the is'oheptanes or isooctanes are excellent motor fuels. Accordingly, in the compounding of motor fuels, it is desirous to convert nheptane into isoheptanes or n-octane into isoctan'es.

Again in the case of the butanes, isobutane is suitable for alkylation and can be alkylated with an olefin to form an excellent motor fuel. "On the *oth'erhand, -11- butane cannot be alkylated by conventional procedures to'form a satisfactory motor fuel. It is thcre fore seen that it is desirable to isomeri'ze n butane to isobutane. Moreover, it is desirable to isomerize methylcyclop'entane to cyclohexane. The cyclohexane can then be oxidized to adipic acid, which finds great utility in the'manufacture of plastics, such as nylon.

The process of the instant invention relates toa'n improvement in an isomerization process in which a saturated hydrocarbon is isomerized in the presence of hydrogen at a temperature of about 700 to 1100" F.

and a pressure in excess of about '50 pounds per square inch. There is no appreciable consumption of the hydrogen during the course of the process. The isomerization is conducted in the -presence of a s'oli'd catalyst, conventional hydrogenation catalysts being suitable for this purpose. We have discovered 'that by incorporating 'in the charge, in accordance With our invention, a polynucl'ear condensed ring compound of the class disclosed below, cracking during the iso'mer-ization is effectively inhibited. The condensed ring compound is selected from the group consisting of the trin'uclear carbocyclic aromatic com" hydrocarbon to the isomerization temperature of about 700 to 1100 F., and at temperature-below the isomerization temperature. This procedure has the advantage of retarding thermal cracking of the saturated hydrocarbon. Moreover, it is also to be preferred, particutern: O

larly in the case of high molecular weight hydrocarbons,

to maintain the partial pressure of the hydrogen at the reaction pressure in excess of 50 percent of the total pressure.

The feed employed in the process of our invent-ion compounds such as octohydroacridine. hibito'rs can comprise pure compounds such as "those 2,762,854 Patented Sept. 11, 1956 2 comprises-asaturated hydrocarbon. The feed may be a :puresaturated hydrocarbon such as n-butane or a mixture ofsaturated hydrocarbons such as a mixture of n-butane, npentane and Inhexane. Where the feed is a saturated paraffinic hydrocarbon, it is desirable to isom erize a feed comprising a straight chain hydrocarbon such as n butane, n-heptaneor n-octane. However, the process of our invention is equally applicable to the isomeriz'ation of branched chain saturated hydrocarbons suchas 'the'isomerization of'2-m'ethyl heptane to 2,4-di-' 'rn'e'thylhxane. "Moreover, the process of our invention is also applicable to the isomeriz'ation of naphthenic hydrocarbons, such as theis'o'meri'zation of methylcyclopentaneto cyclohexan'e. The preferred feeds in "the process'of our invention "comprise the straight chain saturated 'parafiinic'hydrocarbons having from '4 to 1-2 carbon "atoms.

As heretofore mentioned, the cracking inhibitors 'em- 'ployed inthe process of our invention comprise polynuclear'condensed ring compounds. In particular, these crackinginhibitorsincludetrinuclear carbocyclic aromatic compounds such as anthracene and phenanthrene and also the hydrogenated derivatives of these compounds such asotohydroanthracene. Additional cracking inhibitors which canbe used in the process of our inven- .ti'oh includebinuclear heterocyclic nitrogen aromatic compounds such as "quinoline, isoquinoline, and ind-ole, as well'as hydrogenated derivatives of these compounds such 'ashexahydroqiiinoline. Further cracking inhibitors "which'ca'nbeused in the process of our invention include trinuclear heteroc'yclic nitrogen aromatic compounds such as acridine, carbazol e, phenanthridene, phenazine, phenanthrolinc, and the hydrogenated derivatives of these The cracking inmentioned above, or'mixturesof pure compounds such as a mixture of anthracene and-acridine, or of quinoline and innate. "Moreover, "fuel distillate fractions containing the aforementioned cracking inhibitors can be used provided that -the concentration of cracking inhibitor is maintained- 'w-ithin the limits heretofore mentioned. Examples "o ft hes'e fractions include various coal tar oils, light anthracene oil and other mineral coal tar fractions; cer- "tain highly aromatic petroleum hydrocarbon fractions such-as the residues of hydrocracked West Texas heavy gas oil, catalytic cycle oils and hydroforming bottoms.

As statedhe'retofore, but a'minor amount of the cracking inhibitor should be added. Advantageous results can be secured in some cases with as little as 0.01 per cent by weight of cracking inhibitor or less, and in all cases the amount "of cr ac'kin'ginh-ibitor should not be more than 5 per cent by weight of the feed. Concentrations of cracking inhibitor in excess of 5 per cent by weight of the feed donot result in any further retarding of cracking, and may often lead to contamination and/or excessive carbon lay-down on the catalyst. Preferably the amount of addedcracking inhibitor should be from 0.1 to 3 Weight per cent of the feed, and/or should be adjusted so that it is in vapor phase at the reaction conditions.

The process of our invention is conducted in the presenc'efof a solidca'talyst. Suitable solid catalysts for this perature of about 700 to 1100 F. with a temperature of about 775 to 1000 F. being preferred. High reaction pressures in excess of about 50 pounds per square inch are employed, such as 50, 100, 300, .500, 1000, 1500, 2000,

e or 3000 pounds per square inch or more. It is preferable,

particularly when isomerizing relatively high molecular weight hydrocarbons, that the partial pressure of the hydrogen comprise in excess of 50 per cent of the total re action pressure, although lower partial pressures of hydrogen can be used. As indicated heretofore there is no appreciable consumption of hydrogen in the process of our invention, although in the case of a cracking inhibitor which is not a hydrogenated compound, some hydrogen will be consumed in saturating the cracking inhibitor. Thus, if anthracene is used as the cracking inhibitor, at leasta portion ofit will be hydrogenated to octohydroanthracene with a concomitant consumption of hydrogen. Depending upon the temperature and pressure, there may be some hydrocracking. In addition, at low pressures and high temperatures some aromatization of paraflins :and some dehydrogenation of naphthenes may occur. However, the presence of the cracking inhibitors of our invention materially retards at least such hydrocracking.

By way of example we shall illustrate the process of our invention as applied to the isomerization of n-butane to isobutane. The degree of cracking normally encountered when isomerizing butane was determined by adding with the remaining 20.2 weight per cent comprising cracked and dehydrogenated material such as butenes, propane, ethane and methane. V

In order to illustrate the cracking inhibition effect of anthracene, 56 parts by weight of n-butane and 0.6 parts by weight of anthracene (an-anthracene concentration of about 1.07 weight per cent based on the n-butane) plus similar amounts of tungsten disulfide catalyst and hydrogen. as used in the preceding experiment were charged to the bomb, and the bomb heated to the reaction temperature of about 800 F. for 2 hours as before. The average pressure in the bomb at the reaction temperature was again about 1900 pounds per square inch gauge.

The instant product contained about 26.0 weight per cent of isobutane and 62.2 weight per cent of unreacted n-butane, with but 11.8 weight per cent of cracked and dehydrogenated material. It is to be noted that a portion of the cracked material was derived from the anthracene. It is seen from the foregoing that the addition of about 1 per cent by weight of anthracene based on the n-butane modified the products so as to give a reduction of cracked and dehydrogenated material of the order of about 40 weight per cent.

The foregoing bomb runs were elfected witha .very active catalyst and produced relatively high yields of both isobutane and cracked materials. were also conducted in which a less active catalyst comprising about 17.4 weight per cent of tungsten disulfide impregnated on a synthetic silica-alumina base was substituted for the tungsten disulfide catalyst. When 54 parts by weight of n-butane, 22 parts by weight of catalyst, and approximately the same amount of hydrogen as'used in the afore-mentioned experiments were charged to a bomb, and the bomb maintained at a reaction temperature of about 800 F. for a period of about 4 hours (the pressure at the reaction temperature was about 1870 pounds per square inch gauge), a product consisting of 12.5 weight per cent of isobutane and 77.8 weight per cent of Similar experiments a unconverted n-butane was obtained, with the remaining 9.7 weight per cent comprising cracked and dehydrogenated material.

In an identical experiment in which 61 parts by weight of n-butane and 3 parts by weight of anthracene were charged to the bomb (an anthracene concentration of about 4.92 weight per cent based on the n-butane) a yield of about 11.3 weight per cent of isobutane and 84.9 weight per cent of unreacted n-butane was obtained, with the remaining 3.8 weight per cent of product comprising cracked and dehydrogenated material. It is to be emphasized that at least a portion of this 3.8 weight per cent of cracked material was derived from the anthracene. Similar results have been obtained in analogous experiments involving other feeds such as n-heptane.

It is obvious that our invention may be modified by one skilled in ,the art and it is to be understood that these modifications are included within the appended claims. By way of example, such modifications include the substitution or addition of other catalysts. Moreover, other saturated hydrocarbon feeds, cracking inhibitors, and reaction conditions such as temperature and pressure, than those heretofore indicated that are readily apparent to one skilled in the art may be substituted for those specifically mentioned. It is also to be noted that while we have described the process of our invention as applied to batch procedure, namely bomb runs, it is equally applicable to a continuous procedure, as will readily be apparent to one skilled in the art.

Moreover, when the process of our invention is applied to a continuous procedure, optimum results can be secured by adding the cracking inhibitor to the charge prior to preheating the charge to the isomerization temperature, and at a temperature below the isomerization temperature. The advantage of proceeding in this manner is readily apparent from the fact that when parts by weight of cetane and about 8.75 parts by weight of hydrogen were heated together in a bomb to a temperature of about 800 F. for 70 minutes, sufiicient hydrocracking occurred to give a product comprising about 6.3 weight per cent of gas and 35.8 weight per cent of low-boiling liquid. The presence of but 0.15 weight per cent of anthracene based on the amount of cetane reduced the hydrocracking under these conditions so that the product contained but about 1.4 weight per cent of gas and 11.1 weight per cent of low-boiling liquid. When 0.75 weight per cent of anthracene was present, the hydrocracking was further reduced to give a product containing but about 0.8 weight per cent of gas and 5.5 weight per cent of low-boiling liquid. Similarly, 1 weight per cent of quinoline based on the amount of cetane under identical conditions reduced the hydrocracking to a level where the product contained but 1.1 weight per cent of gas and 8.9 weight per cent of low-boiling liquid. It is seen from the foregoing that thermal hydrocracking as well as catalytic hydrocracking is markedly reduced by the presence of minor amounts of the cracking inhibitors of our invention, and accordingly the avoidance of thermal hydrocracking by the addition of cracking inhibitor to the saturated hydrocarbon feed prior to elevating it to a temperature at which a significant degree of thermal hydrocracking is encountered is to be considered a part of our invention.

The process of our invention permits the isomerization of saturated hydrocarbons without any substantial degree of cracking,even though the isomerization is conducted at relatively high temperatures such as of the order of 700 to 850 F.

We claim:

1. In an isomerization process in which a saturated hydrocarbon is isomerized in the presence of hydrogen without any appreciable consumption of the hydrogen by contact with a hydrogenation catalyst selected from the group consisting of vanadium oxide, molybdenum sulfide,

molybdenum oxide, tungsten sulfide, iron, cobalt, nickel, nickel oxide, iron sulfide, nickel tungstate, and cobalt molybdate at an isomerization temperature of about 775 to 1000 F. and a pressure in excess of about 50 rounds per square inch, the improvement which comprises inhibiting the cracking of said saturated hydrocarbon by adding to it a minor amount of a polynuclear condensed ring compound selected from the group consisting of the trinuclear carbocyclic aromatic compounds, the binuclear heterocyclic nitrogen aromatic compounds, the trinuclear heterocyclic nitrogen aromatic compounds, and their hydrogenated derivatives, the amount of said added polynuclear condensed ring compound being not more than 5 per cent by weight of the saturated hydrocarbon.

2. A process in accordance with claim 1 in which the saturated hydrocarbon is a straight chain hydrocarbon having from 4 to 12 carbon atoms.

3. A process in accordance with claim 1 in which the added polynuclear condensed ring compound is anthracene.

4. A process in accordance with claim 1 in which the added polynuclear condensed ring compound is phenanthrene.

5. A process in accordance with claim 1 in which the added polynuclear condensed ring compound is quinoline.

6. A process in accordance with claim 1 in which the added polynuclear condensed ring compound is acridine.

7. A process in accordance with claim 1 in which the added polynuclear condensed ring compound is indole.

8. A process in accordance with claim 1 in which the polynuclear condensed ring compound is added in an amount of from 0.1 to 3 per cent by weight.

9. A process in accordance with claim 1 in which the polynuclear condensed ring compound is in vapor phase at the isomerization temperature.

10. In an isomerization process in which a saturated hydrocarbon is isomerized in the presence of hydrogen without any appreciable consumption of the hydrogen by contact with a hydrogenation catalyst selected from the group consisting of vanadium oxide, molybdenum sulfide, molybdenum oxide, tungsten sulfide, iron, cobalt, nickel, nickel oxide, iron sulfide, nickel tungstate, and cobalt molybdate at an isomerization temperature of about 775 to 1000 F. and a pressure in excess of about 50 pounds per square inch, and in which the partial pressure of the hydrogen comprises in excess of 50 per cent of the total reaction pressure, the improvement which comprises inhibiting the cracking of said saturated hydrocarbon by adding to it a minor amount of a polynuclear condensed ring compound selected from the group consisting of the trinuclear carbocylic aromatic compounds, the binuclear heterocyclic nitrogen aromatic compounds, the trinuclear heterocyclic nitrogen aromatic compounds, and their hydrogenated derivatives, the amount of said added polynuclear condensed ring compound being not more than 5 per cent by weight of said saturated hydrocarbon.

11. In an isomerization process in which a saturated hydrocarbon is isomerized in the presence of hydrogen without any appreciable consumption of the hydrogen by contact with a hydrogenation catalyst selected from the group consisting of vanadium oxide, molybdenum sulfide, molybdenum oxide, tungsten sulfide, iron, cobalt, nickel, nickel oxide, iron sulfide, nickel tungstate, and cobalt molybdate at an isomerization temperature of about 775 to 1000 F. and a pressure in excess of about 50 pounds per square inch, the improvement which comprises inhibiting the cracking of said saturated hydrocarbon by adding to said saturated hydrocarbon a minor amount of a polynuclear condensed ring compound selected from the group consisting of the trinuclear carbocyclic aromatic compounds, the binuclear heterocyclic nitrogen aromatic compounds, the trinuclear heterocyclic nitrogen aromatic compounds, and their hydrogenated derivatives prior to heating said saturated hydocarbon to said isomerization temperature and at a temperature below said isomeration temperature, the amount of said polynuclear condensed ring compound being not more than 5 per cent by weight of said saturated hydrocarbon.

12. A process in accordance with claim 11 in which the saturated hydrocarbon is a straight chain hydrocarbon having from 4 to 12 carbon atoms.

13. A process in accordance with claim 11 in which the added polynuclear condensed ring compound is anthracene.

14. A process in accordance with claim 11 in which the added polynuclear condensed ring compound is phenanthrene.

15. A process in accordance with claim 11 in which the added polynuclear condensed ring compound is quinoline.

16. A process in accordance with claim 11 in which the added polynuclear condensed ring compound is acridine.

17. A process in accordance with claim 11 in which the added polynuclear condensed ring compound is indole.

18. A process in accordance with claim 11 in which the polynuclear condensed ring compound is added in an amount of from 0.1 to 3 per cent by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,288,477 Montgomery June 30, 1942 2,324,762 Calhoun et al. July 20, 1943 2,406,967 Pines Sept. 3, 1946 2,424,953 Myers et al. July 29, 1947 2,436,484 Pines Feb. 24, 1948 2,468,746 Greensfelder et al. May 3, 1949 2,645,605 Lang et al. July 14, 1953 

1. IN A ISOMERIZATION PROCESS IN WHICH A SATURATED HYDROCARBON IS ISOMERIZED IN THE PRESENCE OF HYDROGEN WITHOUT ANY APPRICABLE CONSUMPTION OF THE HYDROGEN BY CONTACT WITH A HYDROGENATION CATALYST SELECTED FROM THE GROUP CONSISTING OF VANADIUM OXIDE, MOLYBDENUM SULFIDE, MOLYBDENUM OXIDE, TUNGSTEN SULFIDE, IRON, COBALT, NICKEL, NICKEL OXIDE, IRON SULFIDE, NICKEL TUNGSTATE, AND COBALT MOLYBDATE AT AN ISOMERIZATION TEMPERATURE OF ABOUT 775* TO 1000* F. AND A PRESSURE IN EXCESS OF ABOUT 50 ROUNDS PER SQUARE INCH, THE IMPROVEMENT WHICH COMPRISES INHIBITING THE CRACKING OF SAID SATURATED HYDROCARBON BY ADDING TO IT A MINOR AMOUNT OF A POLYNUCLEAR CONDENSED RING COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE TRINUCLEAR CARBOXYXLIC AROMATIC COMPOUNDS, THE BINUCLEAR HETEROCYCLIC NITROGEN AROMATIC COMPOUNDS, THE TRINUCLEAR HETEROCYCLIC NITROGEN AROMATIC COMPOUNDS, AND THIER HYDROGENATED DERIVATIVES, THE AMOUNT OF SAID ADDED POYLNUCLEAR CONDENSED RING COMPOUND BEING NOT MORE THAN 5 PER CENT BY WEIGHT OF THE SATURATED HYDROCARBON. 